One office has a IP Office 7.0 and the other has a Partner ACS. If you have a third party endpoint license for the IP Office and you have a VPN connection between the two offices is there any reason you couldn't install a Patton M-ATA at the office with the Partner and plug the RJ11 into an empty trunk port on the ACS? Trying to dial and transfer calls between the offices without using CO trunks.